Thermally-isolated high-speed bobbins



June 22, 1965 R. J. GUERIN ETAL 3,190,580

THERMALLY-ISOLATED HIGH-SPEED BOBBINS Filed Feb. 26, 1963 2 Sheets-Sheet 1 Ill! ATTQRNEYS June 1955 R. J. GUERIN ETAL 3,190,580

THERMALLY-I SOLATED HIGH-SPEED BOBBINS Filed Feb. 26, 1963 2 Sheets-Sheet 2 PRIOR ART PRIOR ART FIGS INVENTORS 2 Robert J Gael-in BY Eo mano H GUEILIQLZZ a alzc lw am, W WW ATTORNEYS United States Patent "ice 3,199,586 THERMALLZ-EUEATEE) HiiGH-SPEED BGEBTNS Robert 5. Guerin, Providence, and Edmond H. Guerin, lira,

Woonsocket Rh, assignors to American Paper Tube Company, WVoonsoc-lret, KL, a corporation of Rhode Island Filed Feb. 26, 1963, Ser. No. 261,115 2 Claims. (Cl. 242118.32)

The present invention relates to improvements in highspeed supports for yarn and like textile materials, and, in one particular aspect, to novel and improved plastic bobbins of precise but inexpensive composite construction wherein destructive effects of heat generated at bearing sites are circumvented by interposed paper inserts which provide protective insulation and bearing surfaces.

As is well known in the textile machinery art, packages of yarn or other textile threads are commonly collected upon spindle-mounted tubular cores or bobbins for further processing and dispensing, it being important that such bobbins be of predetermined external dimensions and smooth surface characteristics, that they be of relatively light weight and low cost, that they be quickly and surely receivable on and removable from their mounting spindles, and that they lend themselves to rotations with and relative slip in relation to high speed spindles. The bobbin and spindle assemblies which have been developed over the course of the years have assumed a variety of structural shapes and have been fabricated of many different materials; one preferred construction, with which the present teachings may be practiced with distinct advantage, involves a generally tubular and conically sloped bobbin which is mated loosely with an associated spindle over substantially its entire length but which is slip-fitted in a clutched or driven relationship with the spindle near one of its ends. Such bobbins are commonly made principally of wood, or of impregnated paper tubing, and large numbers of these are rotated at high speed and are automatically loaded (wound) and unwound in the operations of an active textile plant. Increased productivity, which is an ever-present demand in the industry, has been obtained by running spindles at higher and higher speeds, with resulting heightened frictional losses causing in creased heating at the bearing and clutching sites.

Bobbins which are used at high speeds must be capable of withstanding the very high levels of temperature which are developed out of frictional engagements with the spindles, particularly when the loadings are great and when there are large slippages, such as those occurring shortly after donning. By Way of example, even conventional wooden bobbins may overheat so seriously under these conditions that their precision seating surfaces will char and thereby render the unit useless. These thermal problems have severely obstructed the successful development of molded plastic bobbins, to which the industry has looked forward for some time with the expectation that such bobbins could be produced at relatively low cost and would yet have optimum operating characteristics and physical properties. In this connection, it should be understood that the plastics which have offered the greatest promise, particularly from the standpoints of expense and of ease of molding, are those which possess thermoplastic rather than thermosetting characteristics, and bobbins made of these are quickly deteriorated by high friction-induced temperatures. In other respects, molded thermoplastic materials are exceptionally Well suited to the needs of the bobbin environment; they can be molded to hold dimensions accurately, in intricate configurations, are durable and smooth, and are not particularly susceptible to warping, roughening, chipping, splintering or denting. Unfortunately, the occurrence of highspeed relative movements between outer seating surfaces meas es Patented June 22, 1965 of the metal spindles and inner seating surfaces of thermoplastic bobbins mated with them lead to heating and ultimate softening of the thermoplastic material. In practice, the thermoplastic materials of such bobbins have been known not only to melt at the seating sites but, also, to adhere to the precision spindle seating surfaces and to build up to intolerable accumulations in the form of thick coatings of plastic on the metal spindle.

It is an object of the present invention, therefore, to provide novel and improved textile bobbins of low-cost and uncomplicated construction which causes frictioninduced heating to be inherently suppressed and isolated to extents promoting long operating life at high speeds of rotation.

A further object is to provide unique textile bobbins fabricated primarily of inexpensive materials which are subject to friction-induced thermal damage and which are rendered highly useful under conditions of severe friction by simple and inexpensive inserts.

Another object is to provide novel and improved textile bobbins of low-cost molded thermoplastic material which can be operated at high speeds as the result of unique isolation and suppression of thermal build-ups at sites of friction with spindles.

Still further, it is an object to provide molded thermoplastic textile bobbins in which small and simple paperbased inserts promote improved operations at high speed and obviate the need for precision bearing seats on molded interior surfaces.

By way of a summary account of practice of this invention in one of its aspects, an elongated tubular bobbin member of common external configuration is molded of a conventional thermoplastic molding resin, the interior surfaces of the hollow bobbin being somewhat larger in diameter than the corresponding diameter of the spindle surfaces opposite which they are to be disposed when the bobbin is mated with a spindle for a winding operation. At one localized position axially along the plastic bobbin, a thin short tubular paper insert member is affixed, internally and coaxially. Radial thickness of the insert member is at least about 12 thousandths of an inch, and the interior surfaces thereof are precisely formed to develop a conventional accurate seating with an external bearing surface of a metal spindle. Preferably, the insert member is secured to the interior of the bobbin at the desired location by a suitable adhesive. The paper insert member is preferably formed in the manner of known paper tubing, such as that sometimes used in the fabrication of a tubular bobbin in its entirety, and may be constructed by winding or wrapping a thin impregnated paper sheet in at least two layers about a properly shaped mandrel, the paper being impregnated with a resin which is cured to produce a needed hardness and permanency of other characteristics.

Although the features of this invention which are considered to be novel are set forth in the appended claims, further details as to preferred practices of the invention, as well as the further objects and advantages thereof, may be most readily comprehended through reference to the following description taken in connection with the accompanying drawings, wherein:

FIGURE 1 is a partly cross-sectioned view of a mated high-speed bobbin and spindle assembly including a composite plastic bobbin unit which is well isolated from undue heating in accordance with the present teachings;

FIGURE 2 illustrates the tip of the same assembly, in an enlargement;

FIGURE 3 provides a longitudinal cross-section of an alternative embodiment of thermally-isolated plastic bobbin, wherein the drive by a mated spindle is through spring clutching near the base of the bobbin;

FIGURE 4 portrays a cross-sectioned fragment of a D wooden bobbin of a prior art type in which the seating area has been destroyed by charring induced by friction;

FIGURE is a cross section of the tip of a hardwood bobbin in which susceptibility to thermaldeteriorations is reduced by action of an impregnated paper insert member;

FIGURE 6 depicts softened and damaged interior surfaces of a thermoplastic bobbin of a prior art type which has failed upon operation at high speed;

FIGURE 7 represents the tip of a spindle upon which thermoplastic material has been accumulated in highspeed operation with a plastic bobbin such as that of FIG- URE 6; and

FIGURE 8 illustrates the cross-sectioned tip of a composition bobbin wherein a paper insert member is in protective relationship to a plastic end portion of the bobbin.

The apparatus portrayed in FIGURE 1 includes a spindle structure of a known type wherein a substantially cylindrical metal spindle shaft 9 is rotated about a vertical axis on support bearings (not shown) carried upon the usual textile machine framework with which spindles are associated. Near its lower end, the spindle is driven at high speeds by way of the whirl 10, and, at its upper end or tip, 11, the rotating spindle is tapered and rounded to form a seating surface onto which may be fitted a seating surface of the mated tubular bobbin 12. The sloping and shaping of these respective seating surfaces are such that an essentially line-type small-area contact is developed between them, this being a condition which has been known heretofore to the advantageous in that the bobbin tends to seat itself accurately on the metal spindle and yet does not lock in place so tightly as to impair its dotfing. Driving torques are transmitted from the spindle to the bobbin through the small area of the aforementioned seating contact, and, as expected, there tends to be substantial relative angular slippage during the Winding operation. The same is true of other constructions, in which the area of frictional contacting is relatively broad; friction-induced heating can therefore become very troublesome, especially when both the rotational speeds and loadings are high, and particularly during those intervals after donning when the slippage is very large.

Bobbin 12 is formed of a molded thermoplastic resin, which is relatively inexpensive and yet affords most of the desirable characteristics sought in bobbin constructions. For example, thermoplastic resins can be molded to accurate dimensions and tend to retain these well unless excessively heated. Surface finishes can readily be made highly smooth and durable, and the thermoplastic resin bobbin as a whole strongly tends to resist warping, absorption of moisture, and mechanical damage. While it would naturally occur to the manufacturer that the hollow bobbin interior should be molded with precisely the desired seating surfaces, this type of construction in fact does not prove to be satisfactory when the bobbins are run at high speeds because friction quickly develops high temperatures which soften and deform the seating surfaces. The destructive effects of the friction-induced heating are accelerated when such bobbins are donned and dotfcd frequently. This serious difliculty cannot be resolved by reducing the frictions involved, inasmuch as relatively high frictions are essential to the production of driving torques which cause the bobbins to rotate at high speed. Nor is the problem to be avoided merely by introducing the obvious materials, such as metal, which will become heated but can withstand high temperatures; this is so because the added material then conducts the heat to the nearby plastic and thereby causes it to soften and distort under loadings and stress. For such reasons, the otherwise highly attractive thermoplastic bobbin has not heretofore been suitable for high-speed operation; however, the small tubular paper insert 13 has now provided a full and surprisingly simple and low-cost answer to this serious obstacle to a much-needed breakthrough in this art. As in evident from FIGURES l and 2, the paper insert 13 is in the form of a short thin-walled hollow cylindrical tube which is nested within the hollow thermoplastic bobbin 12 and is affixed to it at an axial position where it is intended that seating with the spindle tip shall occur. In the illustrated structure, the lower edge of the insert makes substantially a line contact with the spindle, along the small-area path designated by dashed line 14, and the pressures and frictional heating are thus highly concentrated at that locus. The insert is preferably abutted with a shoulder 15 (FIGURE 2) molded at a desired locating position within the bobbin, and its exterior is preferably glued or directly molded into attached relationship with thermoplastic material of the bobbin. None of the latter material should be allowed to come into contact with any of the seating surfaces of the spindle, however, else softening and melting can occur, and the insert 13 must therefore project inwardly of the plastic material to leave a radial gap 16 which prevents such contact. Even minute amounts of the thermoplastic material can be highly troublesome, because this softened or melted material collects upon the precision seating surfaces of the spindle and renders them unsuitable for further use. It has been found that the radial thickness of the insert should be at least about 10-12 thousandths of inch for the optimum improvements to be effected, this thickness being equal to about twice the thickness of a good grade of paper used in formation of laminated paper tubing out of which impregnated paper bobbins are commonly fashioned. That thickness thus permits a laminated cylindrical insert to be wound using at least two full turns of sheet paper, about that number of turns being a practical minimum. Thiner inserts do not provide as much thermal isolation as desired, and they also lack important structural strength needed to prevent their distortions while being force-fitted and bonded in place. In those instances when the inner seating surfaces of an insert are to be machined into precise configurations or orientations after the insert has first been secured within the bobbin, the insert must then obviously be of adequate further radial thickness to accommodate also the expected losses of material due to the machining.

Insert 13 serves not only as a mechanical spacer, but as a most effective thermal insulator, or isolator, and bearing. For the latter purposes, which are critical in the present invention, the insert must be highly durable, wearresistant, and non-frangible, must be substantially immune to friction-induced burning, charring or other deterioration of its bearing surfaces, and must have very low thermal conductivity characteristics. The laminated paper tubing fills these requirements when a suitable impregnation of the paper layers imparts a needed hardness; otherwise, compressible paper layers will yield under shock or vibration and will distort intolerably at the bearmg sites. Preferred impregnation is by a thermo-setting resin, which, when cured, insures that the finished tube is dense and hard; alternatively, the cemented paper layers may be filled with another material, such as a high-solidscontent linseed oil, which does not melt and harden upon the spindle tip as the result of heating by friction. The impregnation and lamination of hard paper tubing is of course well known in the bobbin art, and the prior techniques may be exploited for purposes of this invention as well, so long as thermoplastic resins, or like heat-softened materials, are avoided.

In FIGURE 3, the thermoplastic tubular bobbin 17 is of another common type wherein the clutching and angular drive are achieved near the base of the bobbin, through a known spring-clutch connection 18. Longitudinally-extending spring blades of the clutch connection are normally flexed radially outwardly of axis of spindle l9, and are somewhat compressed by the surrounding bobbin, such that the latter tends to be well seated and held in place. Frictional forces associated with this clutch are high, and the impregnated laminated paper insert tube 20 is used to provide the needed protection from thermal injury. In addition, the same bobbin is provided with a further paper-based insert, 21, of like construction, near its outer end and the tip a of the spindle. This added insert serves as a guide and support tending to preserve the bobbin and spindle concentric with one another, and the frictions which are involved there require that the damaging effects of heat of friction be avoided if possible. Similarly, bobbins such as those of FIG- URES 1 and 2 may include further inserts (not illustrated) near their lower ends serving like purposes and advantageously involving the impregnated and laminated tubular paper inserts. Because of the peculiar melting and softening to which the thermoplastic bobbins are susceptible, it is important that the thermoplastic material be prevented from undergoing such changes even at positions where there are no precision seating surfaces; otherwise, the spindle may accumulate unwanted and troublesome deposits of the material even from these positions. Accordingly, at least two such special inserts are desirable within the thermoplastic-bobbins, at axially spaced positions. In other constructions, the paper insert may comprise a single thin and elongated inner tube, extending fully along all the positions at which the friction-induced damage might occur, but in most cases the insert cross-sections at widely-spaced positions must be so different that it is a preferred economical practice to employ two separate paper tube inserts of different diameters.

The remarkable extent of improvements realized with the isolation inserts can be readily perceived in the case of wooden bobbins. Such bobbins, constructed of hardwood (such as maple), have long been considered highly durable and serviceable in the industry. Spindle seating surfaces have been accurately machined directly upon the interiors of these hardwood bobbins and have performed Well during operation at speeds which heretofore have been conventional. However, under the more extreme conditions wherein the present invention is especially advantageous, even the wooden bobbin can fail because of the high localized temperatures which are developed. In FIGURE 4, there is shown a cut-away portion of the tip of a standard type of hardwood bobbin 22 having the same general external configuration as the thermoplastic bobbin 1?; in FTGURES 1 and 2. What had formerly comprised the precision seating area 23 mated with the tip of a driving spindle had, after about 400 successive doffs performed with spindle speeds of 13,000 rpm, been thoroughly distorted and charred to an irregular and unacceptable shape at that site, as shown, such that no further use could be made of the bobbin. The bobbin from which FIGURE 4 has been sketched also included a hard deposit of carbonized debris at 24, this apparently being the result of severe burning which had commenced at about 100 doffs and had resulted in the discharge of white smoke after about 400 doifs, at which point further donning and doffing was necessarily discontinued because of the heat. Burning of the wood was detected after about 100 doffs, with smoking and accumulation of char in the seat area being evident at about 200 doifs. After burning commenced, the seating of the bobbin on the associated spindle changed, until at 400 doifs, the entire short tapered tip of the spindle (such as that of FIGURES 1 and 2) made full contact with the bobbin, as did also a substantial length of the shaft below the tapered tip. The steel spindle tip turned blue under the intense heat which was being generated.

Similar dofing procedures were also followed using another hardwood bobbin, (FIGURE 5), substantially the same in material and external configuration as the hardwood bobbin 22, except that the seating area was occupied by an impregnated and laminated tubular paper insert 26. The inner surfaces of that insert formed bobbin seating surfaces which directly engaged the steel spindle tip being driven at 13,000 rpm. After 400 dotfs, the bobbin became Warm and exhibited only a slight wood odor; at 900 doffs, the bobbin became hot (about 140 F.) but was easy to handle and to dofif, and no bluing of the associated spindle could be noticed (temperature estimated at about 200 F.). Only about a inch axial shift in seating position could be detected after this severe run (900 dofis), and no burning occurred. The improvements wrought by such a special insert are thus seen to be highly significant even when measured in relation to the performance of high-quality wood bobbin.

FIGURES 6 and 7 characterize the serious difficulties which are encountered on both a prior art type of thermoplastic bobbin, 2'7, and its associated spindle, 28, when the friction-induced heating is not avoided. The seating area 29 of the thermoplastic bobbin 27 portrayed in FIG- URE 6 had actually melted after 10 doffs at 13,000 r.p.m., leaving a film 30 of fused thermoplastic material about 10 thousandths of an inch thick on the tapered tip 3 of spindle 28. After about 20 doirs, the seat area 29 became so misshapen and deteriorated as to fail completely as a seat. Spindle accumulations, such as that at 30, prevent proper mating of the spindle with bobbins. A pair of bobbins of like thermoplastic material and configuration, but differing in that one had a diflferent impregnated and laminated tubular paper insert near its tip and base while the other had internal seating surfaces formed of the thermoplastic material itself, were subjected to repeated donning and doffing in relation to spindles rotated at about 13,000 rpm, for purposes of comparison. The bobbin with thermally-isolating inserts became only moderately warm (estimated at about F.) even at about 500 dolfs. The tubular insert near the tip of the protected bobbin possessed a radial wall thickness of about 40 thousandths of an inch, that near the acorn or base of the bobbin being about 75 thousandths of an inch thick. By way of comparison, it was found that the seat area of the plain thermoplastic bobbin fused and caused failure of seat at about only doifs.

Another form of bobbin, a tip portion 32 of which appears in FIGURE 8, includes a large tubular paper barrel 33 which is capped by a special plastic head 34 molded onto one end. Desi-red thermal isolation and protection of the bobbin and of the associated spindles results from the introduction of the laminated and impregnated tubular paper insert 35 at the locus of contacts with the spindles. Insert 35 may conveniently be secured in the desired position by the molding operation.

The lamianted impregnated paper inserts are found to insulate and isolate the thermally sensitive material of the bobbin, and to prevent the contacted steel or aluminum spindle surfaces from being seriously weakened by friction-induced heating. At the same time, the paper of the inserts merely tends to become burnished or polished as the result of slippage in relation to spindle surfaces, and the coefficients of friction needed for proper clutching between the inserts and spindles are found to be highly satisfactory. A minimum axial length of about inch for the special inserts is desirable in that alignment within and adhesion to the bobbin can then be achieved easily. impregnation of the paper with thermosetting resin prevents undue compression which might otherwise tend to change the shape of the insert unacceptably, and the thermosetting resin itself possesses highly desirable characteristics needed in the improved inserts. Although paper inserts are preferred, in some applications the inserts may be molded of a phenolic resin alone, for example. A thermoplastic bobbin equipped near its tip with such a phenolic resin insert 42 thousandths of an inch thick was found to resist friction-induced thermal deterioration at 100 dotfs, although the thermoplastic material surrounding the phenolic resin seat melted and left a deposit upon the spindle below the seat at about 300 dotfs (all at 13,000 rpm. as in the preceding examples). The phenolic seat itself, formed from a flour-filled phenolformaldehyde general purpose molding powder sold under the trade name Durex, No. 791 (Durez Plastics Division of Hooker Electrochemical Company, North Tonawanda, NY.) showed no signs of deterioration, however.

In the fabrication of the impregnated and laminated tubular paper insert members, the paper may first be wound to cylindrical shape upon a mandrel, the impregnating thermosetting-resin varnish being applied subsequently. The varnish may include known phenol-formaldehyde resins, diluted with solvents to the condition in 'which desired paper impregnation can occur readily, An example of the phenol-formaldehyde material is that sold under the trade name Durez No. 1 1897. An alternative is the varnish Bakelite No. 1366. It is preferred that the paper not be fully impregnated and, instead, that the impregnation leave some minute air spaces within the paper; this condition minimizes the thermal conductivity of the inserts. However, these unfilled spaces cannot be so plentiful as to impair dimensional stability and moisture resistance of the inserts.

The molded thermoplastic bobbins which were evaluated in the testing referred to earlier herein involved the materials polystyrene and copolymers of styrene. Additional comparisons have been made of molded bobbins fashioned entirely of the Du Pont Companys thermoplastic material known as Delrin, and of the same material and further protective paper insert members. At the 13,000 rpm. spindle speed, .and with a molded bobbin of Delrin alone in the general top-driven configuration shown in FIGURE 1, failure commenced at the end of twenty-five doffs. This was evidenced by a lowering of the bobbin on its seat. At the end of about one hundred doffs, the bobbing seating gave way completely and operation ceased, there being no significant drive torque imparted to the bobbin by the spindle. Spindle tip temperature appeared to have reached about 150 F. Inspection disclosed that the plastic material at the seating site had been forced to curl away from the heat. Two other bobbins molded of Derlin, each having a laminated and impregnated paper insert carried near the tip, in the manner shown in FIGURE 1, successfully withstood one thousand successive doifs at the same speed and evidenced ample torque and drive. Inspections disclosed that the seats were not materially disturbed and, moreover, that the plastic material surrounding the inserts had not flowed; this was true despite the fact that spindle tip temperature had reached at least 212 F.

Although specific practices have been set forth, and description has been made of preferred embodiments constructed of preferred materials, it should be understood that various changes, modifications, additions and substitutions may be effected by those skilled in the art without departure from these teachings, and it is aimed in the appended claims to embrace all such variations as fall within the true spirit and scope of this invention.

What we claim as new .and desire to secure by Letters Patent of the United States is:

'1. A thermally-isolated bobbing structure for mating with a high-speed rotatable metal spindle, comprising a tubular bobbin molded of thermoplastic material which is susceptible to softening and melting at high temperatures, a thermally-isolating tubular paper seat member including layers of paper wound into a substantially incompressible tube, said layers of said paper seat member being impregnated with varnish which has relatively low thermal conductivity and resists deterioration by frictional contacting with metal surfaces of a spindle rotating at relatively high speeds, said paper seat member being fixed 'within said bobbin in position to engage and seat upon the tip seating surfaces of spindles by which the bobbin is driven, and said paper seat member having a radial thickness of at least about twelve thousandths of an inch at the site where said member engages and seats upon relatively-rotatable tip drive surfaces of spindles, whereby said paper seat member thermally insulates said thermoplastic material of said bobbin from friction-induced heat generated at inner surfaces of said paper seat member and whereby said paper seat member merely tends to become burnished by frictional engagements With the relativerotatable tips of spindles.

2. A low-cost precision thermally-isolated bobbing for mating with high-speed metal spindles, comprising a tubular bobbin member molded entirely of thermoplastic material which is susceptible to softening and melting at high temperatures, a thermally-isolating paper seat member including layers of paper wound into a substantially incompressible tube having an axial length of at least about five-eighths inch, said layers of said paper seat member being impregnated with a thermosetting-resin varnish, said paper seat member being fixed within said bobbin near one end thereof in position to engage and seat upon relatively-rotatable driving and seating surfaces of spindles by which the bobbin is driven, said paper seat member having a radial thickness of at least about twelve thousandths of an inch and mechanically spacing and thermally isolating said thermoplastic material from friction-induced heat generated at inner surfaces of said paper seat member by the relatively-rotatable driving and seating surfaces of spindles.

References Cited by the Examiner UNITED STATES PATENTS 1,811,609 6/31 Bufiington 2421 1831 2,668,020 2/54 Dunlap 242ll8.3 X 2,741,438 4/56 Consoletti 24246.6 2,773,346 12/56 Childs et a1. 57'l'30 X FOREIGN PATENTS 905,269 9/62 Great Britain.

MERVIN STEIN, Primary Examiner. 

1. A THERMALLY-ISOLATED BOBBING STRUCTURE FOR MATING WITH A HIGH-SPEED ROTATABLE METAL SPINDLE, COMPRISING A TUBULAR BOBBIN, MOLDED OF THERMOPLASTIC MATERIAL WHICH IS SUSCEPTIBLE TO SOFTENING AND MELTING AT HIGH TEMPERATURES, A THERMALLY-ISOLATING TUBULAR PAPER SEAT MEMBER INCLUDING LAYERS OF PAPER WOUND INTO A SUBSTANTIALLY INCOMPRESSIBLE TUBE, SAID LAYERS OF SAID PAPER SEAT MEMBER BEING IMPREGNATED WITH VARNISH WHICH HAS RELATIVELY LOW THERMAL CONDUCTIVITY AND RESISTS DETERIORATION BY FRICTIONAL CONTACTING WITH METAL SURFACES OF A SPINDLE ROTATING AT RELATIVELY HIGH SPEEDS, SAID PAPER SEAT MEMBER BEING FIXED WITHIN SAID BOBBIN IN POSITION TO ENGAGE AND SEAT UPON THE TIP SEATING SURFACES OF SPINDLES BY WHICH THE BOBBIN IS DRIVEN, AND SAID PAPER SEAT MEMBER HAVING A RADIAL THICKNESS OF AT LEAST ABOUT TWELVE THOUSANDTHS OF AN INCH AT THE SITE WHERE SAID MEMBER ENGAGES AND SEATS UPON RELATIVELY-ROTATABLE TIP DRIVE SURFACES OF SPINDLES, WHEREBY SAID PAPER SEAT MEMBER THERMALLY INSULATES SAID THERMOPLASTIC MATERIAL OF SAID BOBBIN FROM FRICTION-INDUCED HEAT GENERATED AT INNER SURFACES OF SAID PAPER SEAT MEMBER AND WHEREBY SAID PAPER SEAT MEMBER MERELY TENDS TO BECOME BURNISHED BY FRICTIONAL ENGAGEMENTS WITH THE RELATIVEROTATABLE TIPS OF SPINDLES. 